Polyphenylene ether resin compositions have long been utilized as thermoplastics because they exhibit a variety of beneficial physical and chemical properties which are useful in many applications. Excellent electrical properties, high DTUL as well as inherent flame retardance are three of the prime advantages of polyphenylene ether resins. Despite these advantages, polyphenylene ether resins are not necessarily suitable as molding compositions for many applications without further modification. One of the primary reasons for this is the relatively high melt viscosity of polyphenylene ether resins. A result of this property is relatively poor flow channel exhibited in a typical molding process. Poor flow results in difficulties in molding, losses in manufacturing efficiency as well as poor material performance. For example, in a typical molding process, polyphenylene ethers might have a flow channel of less than twelve inches even at very high temperatures. A glass transition temperature of 210.degree. C. for polyphenylene ethers also indicates that these polymers have characteristically superior thermal properties which may require an element of control in order to provide certain useful products.
A very successful family of thermoplastic products are the modified-polyphenylene ether products wherein the polyphenylene ether base resin is modified or plasticized with another compound in order to provide useful plastic compositions. Typically, modified polyphenylene ethers are comprised of PPE and an alkenyl aromatic compound such as high impact polystyrene. These materials are alloyable in all proportions and provide a variety of products exhibiting advantages of both classes of compounds while minimizing the disadvantages of each. Other plasticization methods are also useful for polyphenylene ether compounds and many conventional plasticizers have been tried. One successful category of such plasticizers has been the triaryl phosphates which are low molecular weight materials which not only tend to plasticize the polyphenylene ethers but also impart an additional degree of flame retardance for these compounds.
Such plasticized modified polyphenylene ether compositions have provided useful products which, however, do not necessarily exhibit the extraordinary thermal properties of unmodified polyphenylene ether. Additionally, some placticized modified-polyphenylene ether compositions tend to experience environmental stress cracking under certain conditions when exposed to stress cracking agents.
In U.S. Pat. No. 4,529,761, which issued July 16, 1985 and is hereby incorporated by reference, Lohmeijer described polyphenylene ether resin compositions which exhibited improved environmental stress crack resistance and which were comprised of polyphenylene ether resins or such resins modified with alkenyl aromatic resins and effective amounts an environmental stress crack resistance agent which was an alkyl or aralkyl sulfonate compound. Lohmeijer did not recognize, however, that such environmental stress crack resistance agents could be utilized in unmodified polyphenylene ether resin compositions (i.e. those which do not contain alkenyl aromatic compounds) and which would thereby provide extraordinarily beneficial thermal properties not otherwise available in modified-PPE systems.
It has now been discovered that the melt behavior of polyphenylene ether resin compositions can be controlled or improved without significantly reducing the inherent thermal properties of such materials and without having to incorporate conventional plasticizers in the compositions. Although conventional plasticizers can improve the melt behavior of polyphenylene ether resins as, for instance, by making them easier to flow in a molding process, they traditionally degrade the other thermal properties of the base resin due to their plasticizing effect. For example, when plasticizers are added to polyphenylene ethers, the flow channel of the resin may increase but the heat distortion temperature of the plastic will generally decrease.
The present invention improves the melt behavior of the polyphenylene ether without conventional plasticizers, therefore, while the flow channel in a molding process will be improved, the heat distortion temperature and thermal stability will not be degraded. The polyphenylene ether resin compositions of the present invention will thereby exhibit good low temperature and high temperature ductility, as well as, excellent hydrolytic stability and the aforementioned excellent electrical properties.
Unmodified polyphenylene ether resin compositions were former non-processable or difficult to process materials. The compositions of the present invention, which exhibit improved flow and melt characteristics while not tending plasticizing the base resin can form the basis of new resin systems which take advantage of these properties.
It is therefore an object of the present invention to provide polyphenylene ether resin compositions which exhibit improved or at least controlled melt characteristics while not generally degrading the inherent advantageous thermal properties of the base resin.
It is a further object of the present invention to provide a process for advantageously controlling the melt behavior of the otherwise difficult to process polyphenylene ether resin compositions.